You can learn about accessing library content from afar, here.
The best place to start if you're looking for library resources that are available digitally is on the library's homepage. There you'll be able to search several library collections at once. Once you drop in keywords related to your topic, you can browse some of the titles that come up in the catalog and in Articles+.
From the results page, scroll down and click "See all catalog results." From the catalog page, you can narrow to items available online by selecting "Online" under Access.
You will also want to look at the databases that PUL subscribes to as you search for other relevant sources. Many are listed under the "Specialized Article Databases" tab, but you may also want to consult the following, which have dramatically expanded their offerings to support research during Covid-19):
